FIG. 1 (Prior Art) is a sectional perspective diagram of a high power Insulated Gate Bipolar Transistor (IGBT) press pack module 1. The module 1 includes a disc-shaped bottom plate member 2 of nickel-plated copper. The disc-shaped bottom plate member 2 has a set of horizontally-extending channels cut into its upper surface, and also has a set of vertically-extending channels cut into its upper surface. As a result of the perpendicularly intersecting channels cut down into the upper surface, the bottom plate member 2 has an array of upward facing pedestals. When viewed from the top perspective, each pedestal has a substantially square planar upper surface. The bottom surfaces of the channels form a two-dimensional grid-shaped surface at the base level 3 of the pedestals (see FIG. 2). A Printed Circuit Board (PCB) 4 is provided that has a circular outer periphery and is of approximately the same diameter as the disc-shaped bottom plate member 2. The disc-shaped PCB 4 also has a set of substantially square cutouts, where the shape of each cutout corresponds to a corresponding one of the pedestals, so that the disc-shaped PCB 4 can be fit down over the pedestals. When the PCB 4 is fit down over the pedestals and is in place, the bottom surface 5 of the PCB 4 rests on the grid-shaped surface 6 of the bottom plate member 2 at the bottom of the channels. Each pedestal of the bottom plate member 2 sticks up through a corresponding cutout in the PCB 4.
FIG. 2 (Prior Art) is a cross-sectional side-view diagram of one of the pedestals 9 of the bottom plate member 2. The PCB 4 that extends around the pedestal 9 is seen in cross-section. The bottom surface 5 of the PCB is seen to be resting on the grid-shaped surface 6 of the bottom plate member 2 at the base level 3 of the pedestal 9.
FIG. 3 (Prior Art) is an exploded perspective view of a holding assembly 7 sometimes referred to as a “cassette”. Cassette 7 includes a four-sided die locator frame 8 made of injection molded insulative plastic. The four-sided frame 8 is open on the bottom and is open on the top so that the frame can fit down over pedestal 9. A silver shim 10 of the cassette assembly fits down into the top of the frame 8 as shown in FIG. 3 and is held in place in the lateral dimension by the frame 8 so that the bottom surface of the silver shim 10 is in contact with the upper square planar surface 11 of the pedestal 9. A first molybdenum shim 12 having a corner cutout fits down onto the upper surface of the silver shim 10. An IGBT die 13 is placed with its frontside 14 down onto the upper surface of the first molybdenum shim 12 so that an emitter contact pad on the frontside 14 of the die 13 is in contact with the top surface of the first molybdenum shim 12. The first molybdenum shim 12 has a corner cutout area so that a spring-loaded contact pin 15 can extend up through the plane of the first molybdenum shim 12 and make contact with a gate contact pad on the downward facing frontside 14 of the IGBT die 13. A second molybdenum shim 16 is placed down onto the backside 17 of the IGBT die 13. The backside of the IGBT die 13 is a metalized collector pad of the IGBT. The second molybdenum shim 16 therefore makes contact with the collector pad of the IGBT die. The stack of shims 10, 12, 16 and the IGBT die 13 is also seen in perspective view in FIG. 2.
One such cassette is fitted over each of the upward extending pedestals of the bottom plate member 2. A disc-shaped top plate member 18 of nickel-plated copper (see FIG. 1) then fits down onto the tops of the cassettes. The flat bottom surface of the top plate member 18 presses down onto the tops of the cassettes, thereby compressing the spring-loaded contact pins of all the cassettes, and forcing good mechanical and electrical contact within each cassette between the bottom of the top plate member, the stack of shims, the IGBT die, and the pedestal of the bottom plate member. Good mechanical and electrical contact is also maintained between the gate pad on the IGBT die, the contact pin, and a metalized track on the top of the PCB 4.
As shown in FIG. 1, the top plate member 18 fits into and is attached to a disc-shaped top lid 19. Top lid 19 is a disc of stamped metal. The top lid 19 and the top plate member 18 may, for example, be brazed together. Likewise, the bottom plate member 2 fits into and is attached to a disc-shaped bottom lid 20. Bottom lid 20 is a disc of stamped metal. The bottom lid 20 and the bottom plate member 2 may, for example, be brazed together. A ceramic collar 21 is attached to the bottom lid 20. A metal flange 26 is attached to the top rim of the ceramic collar 21. During assembly of the press pack module, the top lid/top plate member assembly is pressed down onto the remainder of the press pack module, and the top lid 19 is welded to the flange 26.
The press pack module 1 has a collector terminal 22, an emitter terminal 23, and a gate terminal 24. The collector terminal 22 is an extension of the top lid 19. Within the assembly, the backside collector metal of the IGBTs are electrically coupled through the second molybdenum shims, and through the copper top plate member 18, to the top lid 19. The collector terminal 22 serves as a sensing terminal to the top lid 19. Within the assembly, the frontside emitter pads of the IGBTs are coupled through the first molybdenum shims and the silver shims down to the solid copper bottom plate member 2, and to the bottom lid 20. The emitter terminal 23 serves as a sensing terminal to the bottom lid 20. Within the assembly, the gate pads of the IGBTs are coupled through the spring-loaded contact pins down to a metalized track on the PCB 4, and laterally through the metalized track of the PCB 4 across the module to the inside edge of the ceramic collar, via a clip 25 through a hole in the ceramic collar 21, and to the gate terminal 24. Many IGBT dice may be provided in this way in one press pack module.
Although the cassette is described here as retaining an IGBT die, a cassette can also retain other types of semiconductor dice. A cassette can, for example, contain a diode die. U.S. Pat. No. 6,678,163 discloses a module involving twenty-eight IGBT dice and nine diode dice. The description above of a press pack module is simplified and is presented for background purposes. There are several different variations and types of press pack modules involving cassettes. Rather than using a PCB to provide connection between the gates of the IGBTs and the gate terminal, a preformed insulating insert and stamped copper sheet can be used within the module for gate signal distribution purposes. For additional information on press pack modules and cassettes, see: U.S. Pat. No. 6,678,163 and U.S. Pat. No. 6,303,974 (the subject matter of which are incorporated herein by reference).